Define static pressure, residual pressure, and nozzle pressure in firefighting hydraulics.

• A. Static pressure is the water pressure when no water is moving; residual pressure is the pressure when water is flowing; nozzle pressure is the pressure at the nozzle needed to deliver the intended GPM.
• B. Static pressure is the atmospheric pressure; residual pressure is the pump discharge pressure; nozzle pressure is the pressure at the hydrant.
• C. Static pressure is the pressure in the air; residual pressure is the wind pressure; nozzle pressure is irrelevant.
• D. Static pressure is the pressure in the hose when flushing water; residual pressure is zero; nozzle pressure is the total pressure at the pump.

Answer: (A)

The main idea here is how pressure readings relate to a water stream from the hydrant to the nozzle. Static pressure is the pressure in the system when nothing is moving—water is still, so you’re measuring the available pressure before flow begins. Once you open the line and water starts moving, friction in the hose, across fittings, and any elevation changes reduce that pressure. The pressure you have while water is flowing is the residual pressure. At the nozzle itself, you need a specific pressure to deliver the desired flow rate, and that is the nozzle pressure. You set the pump discharge pressure so that, after losses along the hose path, you still achieve the required nozzle pressure. This definition sequence—static when still, residual during flow, nozzle pressure at the nozzle to deliver the target GPM—is why this answer best fits firefighting hydraulics.